1. Field of the Invention
This invention in general relates to heat exchanger assemblies and more particularly to the routing of capillary tubes to feed refrigerant into the circuits of the heat exchanger.
2. Prior Art
A heat exchanger, as used in an air conditioning system or a refrigeration application, is designed to have refrigerant flowing through tubes and a heat transfer media to be heated or cooled flowing in heat exchange relation with those tubes. In all but the smallest heat exchangers it is common to have more than one fluid flow circuit through the heat exchanger. Hence, it is necessary to make connections to each of the circuits so that they may be arranged in the appropriate configuration.
In refrigeration circuits it is additionally necessary when the heat exchanger is serving as an evaporator that the refrigerant undergo a pressure drop just before entering the circuit such that liquid refrigerant may be evaporated to a gas to absorb heat energy from the media to be cooled. Numerous expansion devices are known in the art to accomplish this pressure drop including a capillary tube. Such a tube is a small internal diameter tube of a predetermined length to achieve the desired pressure drop.
Heretofore, in multiple circuit heat exchangers it has been customary to utilize a capillary tube for each circuit in the heat exchanger and to connect each capillary tube at one end to a distributor and at the other end to each circuit of the heat exchanger. When the circuits of the heat exchanger become numerous the capillary tubes are wound like spaghetti about an end of the heat exchanger, all the capillary tubes originating from one point and terminating at the various circuits. In even more complex applications more than one distributor may be used such that there is considerable intertwining of capillary tubes and the concurrent problems are multiplied. A typical example of a single distributor feeding a series of capillary tubes for a heat exchanger may be found in U.S. Pat. No. 4,057,975. Therein, in FIG. 2 there is disclosed a complex coil having seven circuits, each fed by a separate capillary tube.
It has been found that when numerous capillary tubes are bent around, through, between or among hairpins, return bend headers, feeder tubes and other complex connecting piping at the end of the heat exchanger that these tubes end up in various complex positions, sometimes under stress and in positions where there is potential for the capillary tubes to either rub against an adjacent tube or another capillary tube. During operation of a refrigeration machine the utilization of a compressor or fan or the vibrations involved in transportation may cause the capillary tubes and other piping to rub against each other. Capillary tubes, by their very nature, are small in diameter and have relatively thin walls. Physical contact of a capillary with another component may result in damage to the capillary's function especially if its internal diameter is decreased. Complete failure of the capillary with concommitant failure of the refrigeration circuit caused by leakage of refrigerant may result from a capillary tube rubbing another object.
The present capillary tube arrangement allows the individual capillaries to be mechanically formed into a predetermined configuration prior to being integrated into the heat exchanger. Previous arrangments required individual manual forming of each capillary tube which was both time consuming and fatiguing.
It has also been found in units with complex capillary tube circuiting that the service or repair person may not be able to ascertain which capillary tubes are working properly by detecting the individual temperature thereof. It is conventional to place a hand on a capillary tube to ascertain its temperature to determine whether or not it is blocked. When many capillary tubes are located in a close region, it is impossible or very difficult to ascertain the temperature of each individual tube since heat energy is transmitted between them.
The capillary tube arrangement as disclosed herein incorporates a liquid header with the capillary tubes formed in a tightly wound spiral or helical configuration about the header. The header is mounted parallel to the piping end of the coil such that a neat arrangement of capillary tubes may be formed about the liquid line header. The location of the header is such that the capillary tube merely connects openings spaced along the header to the appropriate circuits spaced along the heat exchanger. The relative position of the header to the circuits of the heat exchanger acts to reduce the overall distance between openings to be connected. Since the overall length of a capillary of a predetermined internal diameter is a function of the desired pressure drop the distance between the liquid header and the circuit to be connected thereto must be less than this length. The length of a capillary tube greater than the distance between the header and the circuit is formed by winding the capillary tube into a helical configuration about the liquid line header such that the design length of the capillary tube is maintained the same and the location of that tube is tightly configured in a known location out of the way of the piping. This compact, neat arrangement provides for the elimination of the potential of rubbing among the various other components as is found when all the capillary tubes originate in a single distributor. Additionally, by separating the capillary tubes along the liquid header, it is possible for the service person to individually detect the temperature of each since they are spaced far enough apart so that the temperature of each may reflect whether or not that capillary tube is functioning properly. Consequently, the service person can place his hand on the capillary tube to ascertain whether or not it is hot or cold depending upon the operation of the unit.